This invention relates to air nozzle apparatus for use in drawing glass fibers, and more particularly it is concerned with an air nozzle apparatus for directing air flow against the undersurface of an orifice plate of a glass fiber drawing forehearth.
Heretofore, methods have been known for drawing glass fibers through an orifice plate by directing air flow against the undersurface of the orifice plate of a glass fiber drawing forehearth, and typical of such method is shown in U.S. Pat. No. 3,905,790, for example. The method disclosed in this document relates to drawing of glass fibers through the orifice plate of flat undersurface at which cones of molten glass are formed as molten glass flows through orifices which are formed close to one another to such an extent that the cones are likely to join one another to wet the undersurface of the orifice plate to cause flooding of the undersurface to occur, and contemplates, in such drawing of glass fibers, directing bulk flow of air against the undersurface of the orifice plate to reach the undersurface of the orifice plate in order to stabilize the cones and cool same as well as to eliminate stagnant gas that might remain in close proximity to the orifice plate and to supply gas to compensate for the gas that is carried away downwardly by the drawn fibers. This method can also have application in the production of glass fibers by means of what is generally referred to as a tip nozzle plate.
One example of the air nozzle apparatus suitable for use in directing air flow against the undersurface of the orifice plate in carrying out the aforesaid glass fiber drawing method is disclosed in U.S. Pat. No. 3,986,853. This air nozzle apparatus comprises a plurality of inlet pipes for introducing air into the nozzle apparatus under uniform pressure, an air nozzle body into which the air is introduced through the inlet pipes, and a single continuous aperture for directing an air current against the orifice plate.
Some disadvantages are associated with the air nozzle apparatus disclosed in this U.S. patent. The single aperture for directing the air flow against the undersurface of the orifice plate is large in dimension, so that the air flow directed against the undersurface of the orifice plate has its pressure reduced and makes it impossible to achieve the desired cooling effect because air presure, rather than the volume of air, is instrumental in achieving cooling satisfactorily. If an attempt is made to increase the air volume to provide improved cooling effect, then the incidence of a break-out of the filaments increases.
To obviate the aforesaid disadvantages of the prior art, an air nozzle apparatus shown in U.S. Pat. No. 4,159,200 has been developed. This air nozzle apparatus comprises a plurality of independent tubular nozzles secured by a fixing member in spaced-apart relation in a single row. By using the plurality of tubular nozzles which are independent of and separate from one another in place of the single air outlet aperture of a large dimension, the air nozzle apparatus has succeeded in providing improved cooling effect by raising the pressure of the air flow directed against the undersurface of the orifice plate.
U.S. Pat. no. 4,149,865 discloses an air nozzle apparatus which, like the air nozzle apparatus disclosed in U.S. Pat. No. 4,159,200, comprises a plurality of independent tubular nozzles arranged in spaced-apart relation in one row. Additionally, the air nozzle apparatus comprises valve means mounted in each of channels connecting the tubular nozzles to a manifold to control the flow rate of air through each channel independently. Like the air nozzle apparatus disclosed in U.S. Pat. No. 4,159,200, the air nozzle apparatus disclosed in U.S. Pat. No. 4,149,865 can achieve improved cooling effect as compared with the air nozzle apparatus shown in U.S. Pat. No. 3,986,853 in that the air flow is ejected through a plurality of tubular nozzles which are independent of and separate from one another.
In each of the air nozzle apparatus described hereinabove, the use of tubular nozzles (pipes) as nozzle elements make it necessary to form bores in a fixing member or a support block in suitable positions to firmly secure them in place. This makes it necessary to provide a boundary wall of a predetermined thickness between the bores to obtain necessary strength for securing and supporting the tubular nozzles. Also, attention has to be paid to the fact that the tubular nozzles themselves have a thickness of their own. Thus, it is impossible to reduce the spacing between the nozzle channels of the adjacent tubular nozzles below a predetermined level, so that the construction of the air nozzle apparatus does not lend itself to the purpose of achieving improved cooling effect by increasing the density of the number of air currents ejected through the tubular nozzles. Also it is a time-consuming operation to fabricate and assemble the air nozzle apparatus of such a construction.
U.S. Pat. No. 4,159,200 also discloses the technical concept of imparting an elliptic cross-sectional shape to the tubular nozzles and arranging the tubular nozzles of this cross-sectional shape in such a manner that the minor dimension of the ellipsis is parallel to the longitudinal direction of the orifice plate, so as to enable uniform cooling effect to be achieved over a wide range widthwise of the orifice plate which is aligned with the direction of the major dimension of the ellipsis of the tubular nozzles. This technical concept can have application in U.S. Pat. No. 4,149,865 as well. In this case, as viewed lengthwise of the orifice plate, the tubular nozzles can be increased in number because they are elliptic in cross-sectional shape thereby to increase the density of the number of the air currents. However, the fact remains unaltered that the tubular nozzles (pipes) are used, so that the problem that the aforesaid limitations placed on the construction interferes with the increase in the density of the number of the air currents still remains unsolved.
To form tubular nozzles of an elliptic cross-sectional shape, it is necessary, as disclosed in U.S. Pat. No. 4,159,200 to flatten tubes by means of a press or to render tubes into elliptic tubes by heating same by means of a burner over a die. The production is thus troublesome and time-consuming, and there are limits to the cross-sectional shapes that can be selected, making it difficult to obtain a desired cross-sectional shape in a nozzle. When tubes are deformed into tubular nozzles of an elliptic cross-sectional shape, it is necessary to form, on a fixing member or a support block for securing same in place, bores of the same shape as the cross-sectional shape of the tubular nozzles. Forming bores of a shape other than the circular shape is a rather difficult operation to perform, thereby making it difficult to fabricate and assemble the air nozzle apparatus.
In U.S. Pat. No. 4,149,865, the valve means comprises a valve core of a cylindrical shape inserted in a valve bore crossing the valve channel for longitudinal and rotational movement in the valve bore, the valve core being formed thereacross with an opening of substantially the same diameter as the valve channel so as to enable same to be aligned with the valve channel by the longitudinal and rotational movement of the valve core, and means for manipulating the valve core from outside for longitudinal and rotational movement thereof. The valve means of this construction enables the operator to effect fine adjustments of the flow rate of the air current ejected through the nozzle channel of each tubular nozzle while observing the drawing of molten glass directly in the vicinity of the orifice plate instead of performing remote control of the flow rate of the air currents, thereby achieving the good effect in cooling the orifice plate.
However, the valve means shown in U.S. Pat. No. 4,149,865 makes it necessary to form in the substantially cylindrical valve core the opening which crosses the valve core. To allow the air current to flow smoothly to the nozzle channel, it is not desirable that the valve channel be smaller in diameter than the nozzle channel, and the opening formed in the valve core should not also be smaller than the nozzle channel in diameter. Thus, the valve core should have a sufficiently large diameter to allow such opening to be formed therein, and this makes it difficult to obtain compact size of the valve means and reduce the spacing interval between the adjacent valve means below a predetermined level. Thus, the spacing interval between the adjacent nozzle channels or the adjacent tubular nozzles also cannot be made smaller than a predetermined level, so that the construction does not lend itself to the purpose of increasing the cooling effect by increasing the density of the number of air currents each flowing through one of the nozzle channels.
In the nozzle apparatus shown in U.S. Pat. No. 4,149,865, the valve means each mounted for one of the nozzle channels are arranged in one row. This also makes it necessary to provide a relatively large space for mounting the valve means, and makes it impossible to reduce the spacing interval between the adjacent nozzle channels, placing limitations on realization of uniform cooling of the orifice plate by increasing the density of the number of the air currents ejected through the nozzle channels.
Another problem raised by the air nozzle apparatus of U.S. Pat. No. 4,149,865 is that, in order to avoid contact between the manipulating portion of the valve means for manipulating same from outside and glass filaments being drawn through the orifices of the orifice plate, the air nozzle apparatus has to be mounted in a manner to tilt with respect to the surface of the orifice plate.
More specifically, an air nozzle apparatus is generally arranged to have its length coincide with the length of the orifice plate and located rearwardly of a group of filaments being drawn in such a manner that the manipulating portion of each valve means for actuating same from outside is directed toward the filaments, and the manipulation of the valve is carried out from the side of an operation passageway located opposite the air nozzle apparatus with respect to the group of filaments. The manipulation portion of each valve means for actuating same from outside comprises a projection located below the air nozzle section. Thus, to avoid contact between the projection and the filament, it is inevitable that the air nozzle apparatus be mounted in a tilting position with respect to the surface of the orifice plate.
However, the arrangement whereby the air nozzle apparatus is mounted in the aforesaid tilting position raises the problem that achieving of uniform cooling of the orifice plate is interfered with. More specifically, when glass filaments are formed by drawings molten glass through the orifices in the orifice plate, ambient air is drawn by rapid movement of the glass filament so that induced air currents directed toward the group of glass filaments being drawn are formed in the vicinity of the orifice plate. These induced air currents impinge on air flow which is directed from the air nozzles against the undersurface of the orifice plate and changes the direction of the air flow as it strikes the undersurface of the orifice plate to escape toward the periphery of the orifice plate. If the air nozzles are greatly tilting, a horizontal component of the air current increases and the air flows from the rear of the orifice plate toward the front thereof. The air current joins the induced air currents to form a strong horizontal air current, so that overcooling of the glass cones located in the rear of the orifice plate results which causes a break-out of the filaments to occur. Thus, to minimize adverse effects of the induced air currents and achieve uniform cooling of the orifice plate, the air nozzle apparatus is preferably mounted in a manner to be substantially perpendicular to the undersurface of the orifice plate as much as possible.